This invention contains a number of improvements to the portable crane described in U.S. Pat. No. 5,224,612. Previously, a number of improvements for machines capable of lifting heavy objects onto rooftops have been proposed. However, such mechanisms have had limited load capacity, limited lifting height, have been overly mechanized, and required large amounts of access. Excepting the said portable crane, these machines require special installation, extensive setup and operation and, are expensive.
A need has thus arisen for a more practical mechanism suitable for hoisting a heavy, bulky object, such as for example, an air conditioner condensing unit onto a roof, without the need for special installation or a heavy counterweight with improved capacity, stability and ergonomics. Such improvements allow for a more stable design, increased durability of parts, faster setup, increased load capacity and operator convenience. Such a mechanism requires good reliability, reduced costs of operation and easy setup.